This invention relates to a coating composition. More particularly, this invention relates to a low-toxic antifouling coating composition for inhibiting the adhesion and growth of underwater organisms on the surface of ships, port facilities, buoys, pipelines, bridges, submarine bases, excavators for submarine oil fields, raceways in power plants, culture nets, fixed shore nets etc. (hereinafter referred to briefly as underwater structures).
In the sea, rivers, lakes and marshes many underwater organisms such as acorn barnacles, sea squirts, serpula, Mytilus edulis, fresh-water mussels, Bugula neritina, green laver or sea lettuce present fouling problems with respect to the above underwater structures and the adhesion and growth of these organisms on the surface or on the splashed parts of the underwater structures cause considerable damages.
For example, when organisms adhere to ships' hulls, the frictional resistance increases and the sailing speed decreases, and thereby maintaining a fixed speed results in increased fuel consumption. This gives rise to economical disadvantage.
In the case where underwater organisms adhere to port facilities, the materials therof are often eroded.
Where the organisms adhere to culture nets or fixed shore nets, the mesh of these nets become blocked.
Hitherto, for the purpose of inhibiting the adhesion and growth of underwater organisms, antifouling coating compositions containing a highly toxic antifouling agent, such as organotin or cuprous oxide have been coated to the surface of underwater structures, so that the adhesion and growth of underwater organisms could be inhibited.
However, the highly toxic antifouling agents are harmful to environmental safety and hygiene when these coating compositions are produced or actually used.
Moreover, these highly toxic antifouling agents gradually dissolve out of the coating composition film formed on the surface of the underwater structures, thereby causing water pollution and unfavorable effects on desirable underwater life such as fish, shellfish etc.
Accordingly, the development of antifouling coating compositions which exert excellent antifouling effects over a prolonged period, and are of low toxicity to humans and desirable underwater life have been strongly demanded.
The present inventors have conducted studies to obtain coating compositions which are of low toxicity to humans and desirable underwater life, yet exhibit strong antifouling activity against underwater organisms.
As a result, the present inventors have found that two compounds as explained hereinafter are very safe, yet exhibit excellent antifouling effects. These findings were followed by continued studies, which have culminated in the present invention.